Polypropylene is very useful in industrial point of view and has various industrial applications, particularly it is widely applied to materials used in automobiles and electronic products, etc. for various usages. However, in order to even further broaden the applications of polypropylene, it is still needed to make an improvement in rigidity and processability which can be led by increasing a stereoregularity and widening a molecular weight distribution.
For polymerization of olefins such as propylene or the like, a solid catalyst comprising magnesium, titanium, an electron donor and halogen as essential elements is known in this field of art, and methods for polymerizing or copolymerizing olefins which use a catalyst system comprised of said solid catalyst, an organoaluminum compound and an organosilicon compound have been proposed many. However, such methods are not satisfying in terms of obtaining polymers having high stereoregularity with a high production yield, and thus needed to be improved in the above aspect.
As a method so as to reduce the production cost by increasing the catalyst polymerization activity and improve physical properties of the resulted polymers by improving the catalyst performance such as stereoregularity, it is generally known in this field of art to use diester of aromatic dicarboxylic acid as an internal electron donor and related patent applications have been filed many. For examples, U.S. Pat. No. 4,562,173, U.S. Pat. No. 4,981,930, Korean Patent No. 0072844 and the like. The above patents describe a method for preparing a catalyst showing high activity and stereoregularity by using aromatic dialkyldiesters or aromatic monoalkylmonoesters. However, the methods of said patents cannot provide high stereoregular polymers with a high yield to the satisfying degree and thus still needed to be improved.
There have been many approaches to increase the molecular weight distribution of a polymer. For example, U.S. Pat. No. 6,376,628 B1 proposes a method for broadening the molecular weight distribution by polymerizing propylene by using a solid catalyst component composed of magnesium, titanium, halogen and an electron donor, in the presence of an organoaluminum compound and an isoquinoline silicon compound, and this method is needed to be improved in terms of catalyst activity and flowability.
WO 00/63261 proposes a method for producing polymers having high stereoregularity and wide molecular weight distribution by using succinates as an internal electron donor, however, it fails to disclose an example of using dialkylalkylidene succinate. Further, said method still needs to be improved in molecular weight distribution.